CVE-2023-36811 is a medium-severity (CVSS 4.7) CWE-347 vulnerability in borgbackup. A fix is available for borgbackup — see the affected versions and patch details below.
Archive spoofing vulnerability in borgbackup
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-36811.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2023-36811 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
borgbackupReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
A flaw in the cryptographic authentication scheme in borgbackup allowed an attacker to fake archives and potentially indirectly cause backup data loss in the repository.
The attack requires an attacker to be able to
- insert files (with no additional headers) into backups
- gain write access to the repository
This vulnerability does not disclose plaintext to the attacker, nor does it affect the authenticity of existing archives.
Creating plausible fake archives may be feasible for empty or small archives, but is unlikely for large archives.
Affected are all borgbackup releases prior to 1.2.5.
Note: CVSS scoring model seemed to badly fit for this case, thus I manually set score to "moderate".
Patches
The issue has been fixed in borgbackup 1.2.5. But there was a bug in 1.2.5 upgrade instructions, thus 1.2.6 with an important fix in docs and code was released a day afterwards.
Additionally to installing the fixed code, users must follow the upgrade procedure as documented in the latest version of the change log.
Workarounds
Data loss after being attacked can be avoided by reviewing the archives (timestamp and contents valid and as expected) after any "borg check --repair" and before "borg prune".
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | borgbackup | all versions | 1.2.5pip install --upgrade 'borgbackup==1.2.5' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for borgbackup, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update borgbackup to 1.2.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-36811 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-36811 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-36811. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2023-36811 in your dependencies?
O3 Security finds CVE-2023-36811 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.